Rick Mascagni and Kylie Cater

Transcription

1 Influence of Hybrid, Seeding Rate, and Nitrogen Fertilizer Rate on Yield Performance of Two Corn Hybrids Differing in Ear Flex Under Varying Soil Moisture Conditions on Mississippi River Soils Rick Mascagni and Kylie Cater Introduction The cost of producing corn has increased dramatically over the last few years. Much of this increased cost has been associated with higher nitrogen (N) fertilizer and seed costs. Optimum N and seeding rate depends on many factors including hybrid, yield potential, soil type, and soil moisture status. Higher seeding rates and N rates are generally needed at higher yield potentials. Another important factor is hybrid genetics. Seed companies are developing hybrids with higher and higher yield potential that may require higher N fertilizer and seeding rates. Fixed-ear type hybrids (determinate) may respond more to higher seeding rates than flex-ear hybrids (indeterminate). This may also affect optimum N rates. To maximize yield potential and profitability, more information is needed on optimum seeding rates and N requirements for the commercial hybrids currently being marketed. Procedures Field experiments were conducted in 2013 on Sharkey clay and Commerce silt loam at the Northeast Research Station (NERS) near St. Joseph to evaluate the influence of seeding rate and N rate on two corn hybrids differing in ear developmental traits. Two hybrids, five seeding rates, and four N rates were evaluated. Hybrids evaluated were Dekalb DKC66-97, a fixed-ear hybrid, and REV 28HR20, a flex-ear hybrid. Seeding rates were 26,400, 30,800, 35,200, and 39,600 seed/acre with targeted plant populations of 24,000, 28,000, 32,000, and 36,000 plants/acre. Seeding rates were increased approximately 10% greater than the targeted population. Seeding rate treatments were planted with a John Deere 1700 precision planter. Nitrogen rates evaluated were 100, 150, 200, and 250 lb/acre on Commerce and 200, 250, 300, and 350 lb/acre on Sharkey. Nitrogen was knifed in using solution at approximately the 2-leaf growth stage. Treatments on Sharkey clay were evaluated under dryland and irrigated conditions. The irrigated trial was furrow-irrigated whenever moisture deficits occurred. Trials were planted March 21. Cotton was the previous crop and cultural practices as recommended by the LSU AgCenter were followed. Experimental design was a randomized complete block with a split plot arrangement of treatments with three replications. Main plot was hybrid and split plots were seeding rate and N rate factorially arranged within each soil moisture regime. Measurements included grain yield (machine harvested two center rows of four-row plots), which is reported at 15.5% moisture, and yield components, plants/acre, seed weight, and kernels/ear. Plant population was determined just prior to harvest. Statistical analyses were performed using the GLM procedure of SAS at probability level of Results and Discussion Sharkey clay: Rainfall was below normal in June (Table 1), resulting in four furrow-irrigations beginning June 1 and terminating July 5. Data for the Sharkey trial is presented in Figs Targeted plant populations ranged from 24,000 to 36,000 plants/acre with actual harvest plant populations ranging from about 26,000 to 34,500 plants/acre (Fig. 1). For flex-ear hybrid (REV 28HR20) yields were maximized when not irrigated at the lowest seeding rate (about 26,000 plants/acre). Yields only ranged from to bu/acre across seeding rates (Fig. 2). On the other hand, yields increased

2 from to bu/acre as seeding rates increased for the fixed-ear hybrid (DKC6-97). There was not a wide divergence in yields between the dryland and irrigated trials, with average yields ranging from to bu/acre in the non-irrigated trial and to bu/acre in the irrigated trial. Unlike the dryland trial, yields under irrigated conditions increased as seeding rates increased for the flex-ear hybrid, ranging from to bu/acre. Yield potential and responses to seeding rate for the fixed-ear hybrid were similar regardless of soil moisture status. Yields increased as seeding rates increased, regardless if dryland or irrigated. Influence of hybrid and seeding rate on ear size (kernels/ear) at two soil moistures is presented in Fig. 3. Generally, ear size decreased as seeding rate increased. However, the rate of decrease was greater for the flex-ear hybrid compared to fixed-ear hybrid, particularly when soil moisture was limiting. These differences may have been greater if drought conditions were more severe. Yield responses to N rate across seeding rates depended, to a large extent, on hybrid (Fig. 4). For both non-irrigated and irrigated trials, N responses across seeding rates were much greater for the flex-ear compared to fixed-ear hybrid. Yields continued to increase with N rate for the flex-ear hybrid, while there was only a small yield increase for the fixed-ear hybrid. Optimum N rate was similar for the flex-ear hybrid, regardless of soil moisture status. Commerce silt loam: Although June rainfall was low in this dryland trial, yields were good ranging from to bu/acre. Data for the Commerce trial is presented in Figs Targeted plant populations ranged from 24,000 to 36,000 plants/acre with actual harvest plant populations ranging from about 26,000 to 35,000 plants/acre (Fig. 5). Similar to the Sharkey clay trial, yields continued to increase as seeding rates increased for the fixed-ear hybrid, while the low seeding rate (26,000 plants/acre) maximized yield for the flex-ear hybrid (Fig. 6). Unlike the Sharkey trial, yields tended to be higher for DKC66-97 compared to REV 28HR20. Influence of hybrid and seeding rate on ear size (kernels/ear) is presented in Fig. 7. Ear size was higher for the flex-ear hybrid and decreased greater than fixed-ear hybrid as seeding rates increased. The largest difference in ear size between the two hybrids occurred at the lowest seeding rate. Optimum N rates were similar for the two hybrids (Fig. 8). Preliminary findings from this study suggest that lower seeding rates may be sufficient for flexear versus fixed ear hybrids, depending to some extent on yield potential. However, these lower seeding rates for a flex-ear hybrid may not result in lower N fertilizer requirements. Table 1. Rainfall in St. Joseph, Month Rainfall inches March 2.5 April 5.8 May 6.3 June 2.7 July 7.6 August 0.8

3 Plant population, plants/acre Yield, bu/acre Fig. 1. Influence of hybrid and seeding rate on harvest plant population in non-irrigated (NI) and irrigated (Irr) trials on Sharkey clay at the NERS, 2013 Fig. 2. Influence of hybrid and seeding rate on yield in nonirrigated and irrigated trials on Sharkey clay at the NERS, 2013.

4 Yield, bu/acre Ear size, kernels/ear Fig 3. Influence of hybrid and seeding rate on ear size in non-irrigated and irrigated trials on Sharkey clay at the NERS, DKC66-97-NI DKC66-97-Irr REV 28HR20-NI REV 28HR20-Irr N rate, lb N/acre Fig. 4. Influence of hybrid and nitrogen rate on yield in nonirrigated and irrigated trials on Sharkey clay at the NERS, 2013.

5 Yield, bu/acre Plant population, plants/acre Fig. 5. Influence of hybrid and seeding rate on harvest plant population on Commerce silt loam at the NERS, Fig. 6. Influence of hybrid and seeding rate on yield on Commerce silt loam at the NERS, 2013.

6 Yield, bu/acre Ear size, kernels/ear Fig. 7. Influence of hybrid and seeding rate on ear size on Commerce silt loam at the NERS, N rate, lb N/acre Fig. 8. Influence of hybrid and nitrogen rate on yield on Commerce silt loam at the NERS, 2013.